Lect01 handout

Physics 102: Lecture 1, Slide 1

Welcome to Physics 102!

• Electricity + Magnetism(at the heart of most processes around us:

…in atoms & molecules; living cells)

• Optics

• Atomic Physics

• Nuclear Physics

• Relativity

Please turn cell phones off

http://www.communicationcurrents.com

Physics 102: Lecture 1, Slide 2

Meet the Lecturer

• ________ @illinois.edu

• Research:_____________________________________

_____________________________________

• Office Hours: ______________________

Physics 102: Lecture 1, Slide 3

Course Website• http://online.physics.uiuc.edu/courses/phys102/spring11/• Daily Planner

– what you should be doing and when you should be doing it

• Course Description• Required Materials

– Be sure to register your I-Clicker prior to lecture

• Lectures– posted after the lecture is given

• First Discussion: _________• First Lab: _________• Exam dates: _________

Physics 102: Lecture 1, Slide 4

Course Philosophy

• Read about it (textbook and prelecture)

• Untangle it (lectures)

• Play with it (labs)

• Challenge yourself (homework)

• Close the loop (discussion/quiz)

The order is important!

Physics 102: Lecture 1, Slide 5

Grading

• Preflights & Lectures 50• Homework 100• Lab (Prelab due at start of lab) 150• Discussion 150

– Take-home quizzes; drop lowest 1

• Hour Exams (3 x 100) 300• Final Exam 250 1000

Physics 102: Lecture 1, Slide 6

Prelectures & ACTS

• Do it!

• Answer preflights 50/1000 points– 1 point for honest attempt at preflight.– 1 point for using clicker in lecture (ACTS)

• 2 points/lecture x 25 lectures = 50 points

• Note that there are 28 lectures, so you have some free ones

• Register I-Clicker before lecture

Physics 102: Lecture 1, Slide 7

Physics 101

• Electricity+Magnetism

• Circuits

• Optics

• Modern• Atomic

• Nuclear

• Relativity

Physics 102Content

• Kinematics

• Forces

• Energy

• Fluids

• Waves (Sound)

Macroscopic Microscopic

Prer

equi

site!

Physics 102: Lecture 1, Slide 8

Electric charge & Coulomb’s Law

Physics 102: Lecture 01

Physics 102: Lecture 1, Slide 9

Origin of Charge• Charge is an intrinsic property of matter

• Two types: – Positive Charge: e.g. protons– Negative Charge: e.g. electrons– Opposite charges attract. Like charges repel.– The electric force is what holds stuff together

• Atoms are neutral– Negatively charged electrons “orbit” around

positively charged central nucleus

Physics 102: Lecture 1, Slide 10

Conductors and Insulators

Most things are in between perfect conductor / insulator

Q: How do electrons behave in a perfect conductor?

Q: How do electrons behave in a perfect insulator?

+ +

+ +

++ + + + +

++++

+ ++++

+ charge

Physics 102: Lecture 1, Slide 11

Electroscope (+demo)

• Conduction– Charged rod is brought near scope– Charged rod touches scope transferring some charge– Scope is left w/ same charge as rod

+ +

+ +

++ + + + +

++++

+ ++++

+ charge

+ + + + + + + –

+ +++–

––

–

+ + + + + + +

Physics 102: Lecture 1, Slide 12

Electroscope (+demo)• Induction

– Charged rod is brought near scope– Scope is briefly grounded allowing charge to flow on

(or off) scope– Scope is left w/ opposite charge as rod

- - -

- - - - - - -

––––

– ––––

- charge

–

+ +++–

––

–

+ + + + + + + –

++–

––

– + +

++

+ + + + + + +

Physics 102: Lecture 1, Slide 13

ACTS• A negatively charged rod is used to charge an electroscope

by induction. What is the resulting net charge on the electroscope?

A) positive B) zero C) negative

• If the conducting electroscope were replaced by an insulating ball and then charged by induction as above, what would be the net charge on the ball.

A) positive B) zero C) negative

Physics 102: Lecture 1, Slide 14

Coulomb’s Law

• Force between charges q1 and q2 separated a distance r:

Mag

nitu

de 𝐹= 𝑘𝑞1𝑞2𝑟2

𝐹= 14𝜋𝜀0𝑞1𝑞2𝑟2 𝜀0 = 8.85× 10−12𝐶2/𝑁𝑚2 Or:

𝑘 = 9× 109𝑁𝑚2/𝐶2 “Coulomb constant”

“Permittivity of free space”

Direct

ion

Opposite charges attract, like charges repel

Physics 102: Lecture 1, Slide 15

Coulomb’s Law

F = k q1q2/r2 k = 9x109 Nm2/C2

+ -

r = 1x10-10 m

Qp=1.6x10-19 C Qe = -1.6x10-19 C

Mag

nitu

de

• What is the magnitude of the force on the proton due to the electron in hydrogen?

Physics 102: Lecture 1, Slide 16

ACT: Coulomb’s Law• What is the direction of the force on the

proton due to the electron?(A) Left (B) Right (C) Zero

• What is the direction of the force on the electron due to the proton?

+ -

r = 1x10-10 m

qp=1.6x10-19 C qe = -1.6x10-19 C

Physics 102: Lecture 1, Slide 17

Electric dipoleA positive and negative charge of equal magnitude separated by a (usually small) distance

+

–

HO

++

-

H

–Q

+Q

Ex: water

= =

Physics 102: Lecture 1, Slide 18

ACT

+ -–

An electric dipole is placed near a large negative charge. What is the net force on the two connected charges?

A) Left B) Zero C) Right

Physics 102: Lecture 1, Slide 19

ACT: Induced Dipole

1) Nothing

2) Attracted to charged sphere.

3) Repelled from charged sphere.

–

• An uncharged conducting sphere is hung next to a charged sphere. What happens when the uncharged sphere is released?

Physics 102: Lecture 1, Slide 20

Induced Dipole

• An uncharged conducting sphere is hung next to a charged sphere. What happens when the uncharged sphere is released?

–+

+++

––

–

–

Physics 102: Lecture 1, Slide 21

Demo: Induced Dipole

• An uncharged conducting sphere is hung between a charged sphere and a grounded sphere and held midway between the two. What happens when the uncharged sphere is released?

–

Physics 102: Lecture 1, Slide 22

Summary of Today’s Lecture

• The concept of charge

• Conductors and insulators

• Coulomb’s Law for the force between charges

– Much more on Coulomb’s Law in next lecture

• Electric dipoles (permanent & induced)

𝐹= 𝑘𝑞1𝑞2𝑟2